1. Field of the Invention
The present invention relates to color correction systems for video signals, and in particular, to color correction systems in which either an entire color space or particular points in the space may be altered.
2. Description of the Related Art
Color correction systems for selectively correcting electronic signals representing optical images are well known in the art. Various forms of color correctors are used in many sophisticated video systems. In particular, sophisticated color correctors are used in film-to-video conversion systems, such as telecines. In many cases, and particularly in the case of telecines, color correction is needed to overcome color inaccuracies or nonlinearities introduced by the film or by electronic scanning of the optical film images to produce the corresponding video signals.
Color correctors in such systems often require levels of skill beyond the capabilities of operators or editors. Indeed, color correction is often viewed as more art than science. With the growing use of video systems and the corresponding growth in need for editors for such systems, color correctors which require less skill, while providing equivalent if not better color correction, are needed.
A difficult aspect of color correction involves video signal characteristics, such as hue, intensity and saturation. Some color correction systems essentially use a "painting" type of approach, where each object is separately selected and assigned a particular color. Colorization of black and white films often uses this approach. This type of approach is time consuming and difficult, as it does not allow for all objects of a given color to be modified at once, but rather all must be "painted" separately.
Alternatively, some devices allow for changes to the entire color space, i.e. all reds may be altered, or all blues or all greens. However, it is often desireable to alter only those shades of a color falling within a certain range of the color space, and to alter those shades precisely. While some prior art devices can perform such general alterations, the desired precision is not provided for by the prior art devices, other than the "painting" technology above, and in those cases the process again is a long and difficult one.
Another major difficulty facing editors, or "colorists," is that most color correction circuitry in conventional color correction systems is done in an analog fashion, and is thus not very precise or flexible. If adjustments are made to accommodate one particular parameter being corrected, some or all of the other parameters are usually also affected to varying degrees. Some newer, more sophisticated color correction systems, such as special effects machines, do use some digital designs. However, these machines again do not allow for a global modification of a particular part of the color space.